There might have been 2,600 incidents of unintended acceleration in the last decade, about 600 more than the number of complaints filed by Toyota owners to federal regulators, a House committee says.

Reporting from Washington — Toyota has received nearly 38,000 calls and reports from customers about sudden acceleration problems in its vehicles, many of them flooding in to the automaker after it began recalling its vehicles last September, a congressional panel said Monday.

The reports demonstrate growing concern about the safety issue among Toyota owners, and hint at the possibility that the actual number of sudden acceleration incidents may be higher than previously reported.

Based on the calls and the reports, the House Energy and Commerce Committee, which is holding a hearing on the recalls Tuesday, estimated that there might have been about 2,600 incidents of unintended acceleration in the last decade, or about 600 more than the number of complaints filed by Toyota owners to federal regulators.

The latest estimates were made public as Toyota disclosed Monday that it had received two federal subpoenas, including one from a New York grand jury, indicating that its deepening political and regulatory problems involving the safety of its vehicles have now expanded to include potential criminal and securities investigations.

Toyota said it received a subpoena Feb. 8 from the federal grand jury in the Southern District of New York, requesting "certain documents related to unintended acceleration of Toyota vehicles and the braking system of the Prius." The subpoena was issued to both the company and its subsidiaries.

A second subpoena was issued Feb. 19 by the Los Angeles office of the Securities and Exchange Commission to Toyota Motor Corp., the Japanese parent organization, and Toyota Motor Sales USA, the Torrance-based sales arm for North America. That subpoena was "seeking production of certain documents including those related to unintended acceleration of Toyota vehicles and the company's disclosure policies and practices," the company said in a brief statement.

The units "intend to cooperate with the investigations and are currently preparing their responses," the statement said.

The latest figures for complaints were disclosed in the committee's letter sent Monday to James Lentz, president of the firm's Torrance sales operation. It raised new questions about the adequacy of disclosures and the remedies that the company has promised its customers.

Toyota attorneys privately told the panel that sticking accelerator pedals, which the company has blamed publicly for some of the sudden-acceleration incidents, do not typically cause the acceleration problem, according to the letter, signed by committee chairman Rep. Henry Waxman (D-Beverly Hills) and Rep. Bart Stupak (D-Mich.), chairman of the committee's investigation panel.

A second letter sent to Transportation Secretary Ray La Hood also reports that the federal government has lacked the technical resources and the management commitment to thoroughly investigate the problems and has failed to take seriously the entire problem of sudden acceleration.

The letter says a Toyota official boasted internally that federal safety regulators "either laughed or rolled their eyes in disbelief" when the issue of sudden acceleration came up in a meeting last August.

Toyota did not respond directly to Waxman's letter but issued a statement Monday saying that it was committed to safety and citing a new top-to-bottom quality review of all its divisions.

On Sunday, the House Oversight and Government Reform Committee released internal Toyota documents that showed how company officials boasted of its success in limiting safety recalls that saved it hundreds of millions of dollars, including the curtailing of a recall that involved sudden-acceleration problems in its vehicles.

The document was the first indication that Toyota had orchestrated an effort to limit recalls, even when it knew that it had potentially serious safety problems.

Sudden acceleration has been blamed in 34 fatalities, federal records show. Since last fall, the company has issued 10 million recall notices, with about 2 million vehicles subject to more than one recall.

The Waxman letter lays out evidence that Toyota's official explanation that floor mats and sticking gas pedals are to blame fails to provide a credible understanding of the problem. Based on customer reports to Toyota, floor mats and sticking pedals do not account for 80% of the reports the company has received.

The Waxman letter also attacks a consultant's report that Toyota has used to defend itself from allegations that a hidden electronic defect exists. The report was issued by Menlo Park-based Exponent Inc., based on tests it conducted on behalf of Toyota.

But the committee said experts it has consulted, including University of Maryland engineering professor Michael Pecht, found that Exponent's investigation of the problem was cursory at best and that its methodology lacked scientific vigor.

The letter also questioned Toyota's earlier claim that misplaced floor mats were a major cause of sudden acceleration.

"Our preliminary assessment is that Toyota resisted the possibility that electronic defects could cause safety concerns, relied on a flawed engineering report and made misleading public statements concerning the adequacy of recent recalls to address the risk of sudden unintended acceleration," Waxman wrote.

Nonetheless, Toyota held a conference call on Monday to explain the operation of its electronic throttle system, complete with videos showing how the components are tested by being bombarded with electromagnetic radiation.

The experts said they had found "no evidence" of an electronic problem, despite repeated testing over the last seven years. "The system cannot under any circumstances cause sudden unintended acceleration," said Paul Williamsen, national manager of Lexus College at the University of Toyota in Torrance.